This is the first I've heard of the softcover platform.
After some research it looks like it was posted on HN about 2 years ago, but there's only a handful of books posted on the platform compared to let's say leanpub who has a few thousand.
Since you just posted this book on softcover, it's safe to say you're still happy using it, but why aren't more authors choosing your platform?
You would think after 2 years it would have gained traction, especially considering how big your reach is from previously successful tutorials and books.
I'm a content author and softcover looks nice. My main issue with leanpub is that all sales data is anonymous and you can't obtain e-mail addresses of your readers and your platform seems to solve that.